Semiconductor device having a variable carbon concentration

ABSTRACT

A semiconductor device includes at least one transistor structure. The at least one transistor structure includes an emitter or source terminal, and a collector or drain terminal. A carbon concentration within a semiconductor substrate region located between the emitter or source terminal and the collector or drain terminal varies between the emitter or source terminal and the collector or drain terminal.

TECHNICAL FIELD

Embodiments relate to semiconductor manufacturing technologies and inparticular to a method for forming a semiconductor device and asemiconductor device.

BACKGROUND

Many semiconductor devices comprise semiconductor substrates withregions of different conductivity types and different dopingconcentrations. The implementation of semiconductor substrates withdifferent doping regions is often a challenging task. One way ofgenerating donors within a semiconductor is an implant of protons togenerate hydrogen-induced donors. It is desired to increase the dopingefficiency of donors caused by proton implant.

SUMMARY

Some embodiments relate to a method for forming a semiconductor device.The method comprises implanting a defined dose of protons into asemiconductor substrate and tempering the semiconductor substrateaccording to a defined temperature profile. At least one of the defineddose of protons and the defined temperature profile is selecteddepending on a carbon-related parameter indicating information on acarbon concentration within at least a part of the semiconductorsubstrate.

Some further embodiments relate to a semiconductor device comprising atleast one transistor structure. The transistor structure comprises anemitter or source terminal and a collector or drain terminal. Further, acarbon concentration within a semiconductor substrate region locatedbetween the emitter or source terminal and the collector or drainterminal varies between the emitter or source terminal and the collectoror drain terminal.

Some embodiments relate to a method for forming semiconductor devices.The method comprises implanting a first defined dose of protons into afirst semiconductor wafer and tempering the first semiconductor waferaccording to a first defined temperature profile. At least one of thefirst defined dose of protons and the first defined temperature profileis selected depending on a carbon-related parameter indicatinginformation on a first carbon concentration within at least a part ofthe first semiconductor wafer. Further, the method comprises implantinga second defined dose of protons into a second semiconductor wafer andtempering the second semiconductor wafer according to a second definedtemperature profile. At least one of the second defined dose of protonsand the second defined temperature profile is selected depending on acarbon-related parameter indicating information on a second carbonconcentration within at least a part of the second semiconductor wafer.The first carbon concentration is different from the second carbonconcentration.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of apparatuses and/or methods will be described in thefollowing by way of example only, and with reference to the accompanyingfigures, in which:

FIG. 1 shows a flow chart of a method for forming a semiconductordevice;

FIG. 2 shows a schematic cross section of a semiconductor device;

FIG. 3 shows a schematic cross section of an insulated gate bipolartransistor structure;

FIG. 4 shows a schematic cross section of a Mesa-insulated gate bipolartransistor structure;

FIG. 5 shows field stop profiles with corresponding carbondistributions;

FIG. 6 shows a flow chart of a method for forming a semiconductordevice;

FIG. 7 shows the solubility of carbon in silicon;

FIG. 8 shows the diffusion coefficient of substitutional carbon Cs insilicon; and

FIG. 9 shows the diffusion coefficient of interstitial carbon Ci insilicon.

DETAILED DESCRIPTION

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare illustrated. In the figures, the thicknesses of lines, layers and/orregions may be exaggerated for clarity.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the figures and will herein be described in detail. Itshould be understood, however, that there is no intent to limit exampleembodiments to the particular forms disclosed, but on the contrary,example embodiments are to cover all modifications, equivalents, andalternatives falling within the scope of the disclosure. Like numbersrefer to like or similar elements throughout the description of thefigures.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art.However, should the present disclosure give a specific meaning to a termdeviating from a meaning commonly understood by one of ordinary skill,this meaning is to be taken into account in the specific context thisdefinition is given herein.

FIG. 1 shows a flow chart of a method for forming a semiconductor deviceaccording to an embodiment. The method 100 comprises implanting 110 adefined dose of protons into a semiconductor substrate and tempering 120the semiconductor substrate according to a defined temperature profile.At least one of the parameters defined dose of protons and definedtemperature profile is selected depending at least on a carbon-relatedparameter indicating information on a carbon concentration within atleast a part of the semiconductor substrate.

By selecting the dose of protons for implant and/or the temperatureprofile for the annealing after implant based on a carbon concentrationwithin the semiconductor, the resulting doping concentration and/ordoping distribution may be adjusted more accurate and/or more flexible.Further, substrates with high carbon concentration may be used. In thisway, the doping efficiency may be increased.

Substitutional carbon Cs may be pushed out of the lattice and may becomeinterstitial carbon Ci during the implant of the defined dose ofprotons. The protons may build up proton-induced donors (also calledhydrogen-induced donors or shallow thermal donors) at the latticevacancies prior occupied by the substitutional carbon Cs. Theinterstitial carbon Ci may built up CiOi-H complexes or CiO2i-Hcomplexes (or other C_(x)iO_(x)i-H complexes) with oxygen and hydrogenavailable in the semiconductor. The CiOi-H complexes may have very lowdiffusion constant and may function as shallow thermal donors too.Therefore, the doping concentration may be increased by the CiOi-Hcomplexes. Further, the CiOi-H complexes may bind free hydrogen whichmay otherwise build up higher-order hydrogen complexes at the latticevacancies prior occupied by the substitutional carbon Cs which mayreduce the number of thermal donors. In other words, the CiOi-Hcomplexes may increase the doping concentration by binding freehydrogen.

The semiconductor device may be a silicon-based semiconductor device, asilicon carbide-based semiconductor device, a gallium arsenide-basedsemiconductor device or a gallium nitride-based semiconductor device,for example. The semiconductor substrate may be a silicon-basedsemiconductor substrate, a silicon carbide-based semiconductorsubstrate, a gallium arsenide-based semiconductor substrate or a galliumnitride-based semiconductor substrate, for example. The semiconductorsubstrate may be a wafer, a part of a wafer or a semiconductor die, forexample.

The carbon may be incorporated in the semiconductor substrate in variousways. The carbon may be incorporated during the manufacturing of thesemiconductor substrate itself (e.g., crystal growth or epitaxialdeposition) or after manufacturing of the semiconductor substrate andbefore the proton implant.

For example, the carbon may be incorporated into the at least one partof the semiconductor substrate before implanting the defined dose ofprotons by implanting carbon into at least one part (e.g., field stoplayer or drift layer) of the semiconductor substrate. The implant energyof the carbon implant may be selected so that a desired carbonconcentration and/or carbon profile may be obtained within thesemiconductor substrate.

Alternatively or additionally, the carbon may be incorporated into atleast one part of the semiconductor substrate before implanting thedefined dose of protons by diffusing carbon into at least one part ofthe semiconductor substrate. A diffusion temperature, diffusion timeand/or provided amount of carbon for diffusion may be selected so that adesired carbon concentration and/or carbon profile may be obtainedwithin the semiconductor substrate. For example, carbon exceeding thesolubility limit of carbon at room temperature in the semiconductorsubstrate is provided during the diffusion process. The solubility limitof carbon 710 (Sol_(C)) in silicon for different temperatures is shownin FIG. 7.

Alternatively or additionally, the carbon may be incorporating bygrowing at least one part of the semiconductor substrate with a definedcarbon distribution. In other words, the carbon may already beincorporated during the manufacturing of the semiconductor substrateitself (e.g., crystal growth or epitaxial deposition). In this way, avery homogeneous carbon concentration may be obtained throughout thewhole semiconductor substrate or throughout a deposited layer- or grownpart of the semiconductor substrate.

Independent from the method used for incorporating the carbon into thesemiconductor substrate, a part of the carbon may be diffused outafterwards. In other words, additionally the method 100 may comprisediffusing carbon out of the semiconductor substrate by tempering thesemiconductor substrate according to a defined diffusion temperatureprofile. For example, the semiconductor substrate may be heated to apredefined temperature for a predefined time in an atmosphere withoutcarbon or with carbon at a low level (e.g., significantly below thesolubility of carbon at this temperature) so that carbon diffuses out ofthe semiconductor substrate. In this way, a desired carbon profile(e.g., turtle-shaped profile) may be obtained.

For example, the carbon concentration (e.g., average carbonconcentration or maximal carbon concentration) within at least one partof the semiconductor substrate may be higher than 1*10¹⁵ cm⁻³ (or higherthan 1*10¹⁴ cm⁻³ or higher than 5*10¹⁵ or even higher than 1*10¹⁶ cm⁻³).

Alternatively or additionally, the carbon concentration (e.g., averagecarbon concentration or maximal carbon concentration) may be kept belowan upper limit to control or minimize the described effect. For example,the carbon concentration within at least one part of the semiconductorsubstrate may be lower than 1*10¹⁵ cm⁻((or lower than 1*10¹⁴ cm⁻³ orlower than 5*10¹⁵).

The defined dose of protons may be implanted with a single implantenergy or may be distributed over several implant energies or implantenergy ranges resulting in implant maxima at one or more depths withinthe semiconductor substrate. For example, the defined dose of protons ishigher than 1*10¹³ cm⁻², 1*10¹⁴ cm⁻² or higher than 1*10¹⁵ cm⁻³ orhigher than 5*10¹⁵ cm⁻³).

The defined dose of protons may be implanted from a front side of thesemiconductor substrate. A front side of the semiconductor substrate maybe a side of the semiconductor substrate at which the more complexstructures are to be manufactured e.g., transistor structures and/orwiring) while the back side of the semiconductor substrate may be a sideof the semiconductor substrate at which less complex structures are tobe manufactured (e.g., transistor structures and/or wiring).

For example, the defined dose of protons is implanted 110 into asemiconductor substrate to generate a defined concentration ofinterstitial carbon in at least one pail of the semiconductor substrate.

The tempering 120 may be done with the defined temperature profile ortemperature ramp. The defined temperature profile may define the courseof the temperature over time during the tempering of the semiconductorsubstrate. The defined temperature profile may comprise a maximaltemperature below or less than 500° C. (or less than 550° C. or lessthan 450° C.). The proton-induced donors may be activated during thetempering 120.

The realization of the proton-induced donors and the subsequent processsteps for the realization of the power devices may be performed attemperatures below 500° C. (or below 550° C. or below 450° C.) after theimplant 110 of the defined dose of protons. In this way, diffusion or achange of the carbon distribution and/or hydrogen-induced donors may beavoided or kept low. Optionally, a laser process in a melting ornon-melting mode may be performed at the wafer backside (e.g., for theactivation of a backside emitter for IGBTs or an emitter for diodes or adrain zone for Power MOSFETs) after the proton irradiation which may beuncritical for the proton-induced doping due to the strong localizationof the temperature maximum close to the wafer backside, for example.

The defined dose of protons and/or the defined temperature profile isselected or predefined depending on a carbon-related parameterindicating information on a carbon concentration within at least a partof the semiconductor substrate (e.g., an average or maximal carbonconcentration within a region of interest, for example, drift zone orfield stop, or within the whole semiconductor substrate).

The carbon-related parameter may be the carbon concentration itself(e.g., average or maximal carbon concentration) or a parameterproportional to the carbon concentration or enabling a determination ofthe carbon concentration, for example. For example, the carbon-relatedparameter may be an electrical resistance or doping concentration of thesemiconductor substrate before the implant or of a comparable wafer(e.g., from the same piece of grown semiconductor crystal) afterimplant. The electrical resistance or doping concentration of thesemiconductor substrate may be information indicating a carbonconcentration, since these parameters may be proportional to the carbonconcentration or may enable the determination of the carbonconcentration.

For example, the method may optionally comprise measuring a carbonconcentration (or another parameter indicating the carbon concentration)of at least a part of the semiconductor substrate or a carbonconcentration (or another parameter indicating the carbon concentration)of at least a part of another semiconductor substrate manufacturedtogether with the semiconductor substrate of the semiconductor device tobe formed. The carbon concentration may be measured directly orindirectly (e.g., space-resolved deep-level transient spectroscopyand/or infrared measurement or measuring an electrical resistance ordoping concentration of the semiconductor substrate)

For example, one or more forerunner wafers (e.g., 3) or one or more testwafers may be fully or partly processed. For example, the thermal budgetof the full process may be done (e.g., omitting the trench etching) anda proton implantation. The forerunner wafers or test wafers may bemeasured (e.g., by IR, DLTS, Spreading resistance profiling SRP orelectrical measurement) to determine the doping concentration, forexample, and adapting the process for the remaining wafers. In otherwords, the method may further comprise processing one or more testwafers and determining a carbon-related parameter of one or more of thetest wafers. Further, further wafers may be processed based on thedetermined carbon-related parameter.

Additionally, the method 100 may optionally further comprise implantingelectrons, alpha particles, helium or further protons into thesemiconductor substrate with a defined energy distribution to generateinterstitial semiconductor atoms with a defined depth distribution. Inthis way, the number of resulting CiOi-H complexes may be furtherincreased.

A large variety of semiconductor devices may be manufacturable accordingto the proposed concept or one or more embodiments described above orbelow. For example, semiconductor devices with one or more transistorstructures may be manufactured based on the proposed concept. Forexample, power semiconductor devices (e.g., insulated gate bipolartransistor IGBT or a vertical field effect transistor) or diodes may bemanufactured based on the proposed concept. For example, a powersemiconductor device may comprise a blocking voltage above 100V (orabove 500V, above 1000V or above 1500V, e.g., 600V, 1200V or 1700V).

FIG. 2 shows a schematic cross section of a semiconductor deviceaccording to an embodiment. The semiconductor device 200 comprises atleast one transistor structure. The transistor structure comprises anemitter or source terminal 210 and a collector or drain terminal 220. Acarbon concentration 230 within a semiconductor substrate 240 locatedbetween the emitter or source terminal 210 and the collector or drainterminal 220 varies between the emitter or source terminal 210 and thecollector or drain terminal 220.

An additional degree of freedom for implementing a desired dopingprofile of transistors may be provided by implementing a carbonconcentration varying between the terminals of the transistor.Additionally or alternatively, less protons may be necessary to reach adesired doping concentration, if the carbon concentration is increasedso that the doping efficiency may be increased.

At least one transistor structure may be a bipolar transistor structurewith a collector terminal, an emitter terminal and a base terminal, maybe a field effect transistor structure comprising a source terminal, adrain terminal and a gate terminal or may be an insulated gate bipolartransistor structure comprising an emitter terminal, a collectorterminal and a gate terminal, for example.

The emitter or source terminal 210 and the collector or drain terminal220 may be terminals enabling an electrical connection to otherterminals on the semiconductor device or to terminals of an externaldevice. For example, the emitter or source terminal 210 may be anemitter or source implant region, a pad connected to the emitter orsource implant region or a front side metal layer connected to theemitter or source implant region. For example, the collector or drainterminal 220 may be a collector or drain implant region, a pad connectedto the collector or drain implant region or a back side metal layerconnected to the collector or drain implant region.

An example for a varying carbon concentration is shown next to the crosssection of FIG. 2. The local carbon concentration varies for differentdepths within the semiconductor substrate of the semiconductor device200. For example, the carbon concentration may vary between 1*10¹⁴ cm⁻³and 2*10¹⁶ cm⁻³ (or between 1*10¹⁴ cm⁻³ and 1*10¹⁷ or between 1*10¹⁵cm⁻³ and 5*10¹⁵ cm⁻³). For example, the carbon concentration profilebetween the emitter or source terminal 210 and the collector or drainterminal 220 comprises a maximal carbon concentration of less than2*10¹⁶ cm⁻³ and a minimal carbon concentration of more than 1*10¹⁴ cm⁻³.For example, a maximal carbon concentration of the carbon concentrationprofile may be more than twice (or more than 10 times or more than 50times) a minimal carbon concentration of the carbon concentrationprofile,

For example, the semiconductor device 200 may comprise an increasedcarbon concentration within a drift layer or drift zone of thetransistor structure in comparison to other regions of the semiconductorsubstrate of the semiconductor device 200 or may comprise an increasedcarbon concentration within a field stop layer or field stop zone of thetransistor structure in comparison to a drift layer or drift zone of thetransistor structure.

The semiconductor device may comprise a thin semiconductor substrate.For example, the semiconductor substrate of the semiconductor devicecomprises a thickness of less than 200 μm (or less than 150 μm, lessthan 100 μm or less than 80 μm). For example, carbon may be diffusedinto the semiconductor substrate from the backside (e.g., into a fieldstop zone of the semiconductor device) and/or at least a part of adefined dose of protons may be implanted from the back side of thesemiconductor substrate.

Alternatively, the carbon atoms can be implanted from the front side.For example, this implantation step may be performed at the beginning ofthe fabrication process so that a deep in-diffusion of the carbon atomscan be achieved. Optionally, an additional high temperature step can beperformed between the carbon implantation step and the fabricationprocesses required for the realization of the power device to obtain adeeper penetration depth of the in-diffused carbon atoms, for example.

More details and aspects of the semiconductor device 200 (e.g.,semiconductor substrate, implementing a varying carbon concentration)are mentioned in connection with the proposed concept or one or moreexamples described above or below (e.g., FIGS. 1 or 3 to 6). Thesemiconductor device 200 may comprise one or more optional features inaddition corresponding to one or more aspects of the proposed concept orone or more examples described above or below.

FIG. 3 shows a schematic cross-section of a part of an insulated gatebipolar transistor arrangement 350 representing a transistor structureof a semiconductor device according to an embodiment. The insulated gatebipolar transistor arrangement 350 comprises a semiconductor structure(e.g., silicon-based or silicon carbide-based) comprising a collectorlayer 360, a drift layer 370, a plurality of body areas 380, a pluralityof source areas 385 and a gate 390 of a plurality of gates 390 (e.g., ofsimilar or equal structures distributed over the insulated gate bipolartransistor arrangement). The plurality of source areas 385 and the driftlayer 370 comprise at least mainly a first conductivity type n or p) andthe plurality of body areas 380 and the collector layer 360 comprise atleast mainly a second conductivity type (e.g., p or n). The plurality ofgates 390 are arranged so that the gates 390 are capable of causing aconductive channel 392 between the source areas 385 and the drift layer370 through the body areas 380. The gates 390 may be electricallyinsulated from at least the body areas 380 by an insulation layer 394(e.g., gate oxide layer).

The body areas 380 and the collector layer 360 comprise the secondconductivity type which can be a p-doping (e.g., caused by incorporatingaluminum ions or boron ions) or an n-doping (e.g., caused byincorporating nitrogen ions, phosphor ions or arsenic ions).Consequently, the second conductivity type indicates an oppositen-doping or p-doping. In other words, the first conductivity type mayindicate an n-doping and the second conductivity type may indicate ap-doping or vice-versa.

The plurality of gates 390 may be arranged so that the gates 390 cause aconductive channel 392 between the source areas 385 and the drift layer370 through the body areas 380 according to a field effect transistorprinciple. In other words, the plurality of gates 390 are arranged inthe proximity of the body areas 380 but electrically insulated from thebody area 380 by an insulation layer 390 so that a conductive channel392 between the source areas 385 and the drift layer 370 can becontrolled by a voltage applied to the gates 390.

In other words, the transistor structure may comprise a drift layer 370located between the emitter or source terminal 210 and the collector ordrain terminal 220. Optionally, the transistor structure may comprisealso a field stop layer located between the drift layer 370 and thecollector or drain terminal 220. The field stop layer (also called fieldstop zone) may comprise an average carbon concentration of at leasttwice (or at least 10 times or at least 50 times) an average carbonconcentration of the drift layer 370, for example. This may be realizede.g., by a carbon implantation step with a subsequent drive-in step orby epitaxial deposition techniques.

A semiconductor device 200 may comprise mainly or only the insulatedgate bipolar transistor arrangement or may comprise further electricalelements or circuits (e.g., control unit for controlling the insulatedgate bipolar transistor arrangement or a power supply unit).

More details and aspects of a semiconductor device with one or moreinsulated. gate bipolar transistor arrangements 350 (e.g., semiconductorsubstrate, implementing a varying carbon concentration) are mentioned inconnection with the proposed concept or one or more examples describedabove or below (e.g., FIGS. 1 to 2 or 4 to 6). The semiconductor deviceshown in FIG. 3 may comprise one or more additional optional featurescorresponding to one or more aspects of the proposed concept or one ormore examples described above or below.

For example, the defined dose of protons mentioned in connection withone or more embodiments above or below (e.g., FIG. 1) may be implantedinto the semiconductor substrate by implanting a defined dose of protonsinto a drift layer region of the semiconductor device to be formed,

Additionally or alternatively, carbon may be implanted or diffused orincorporated by epitaxial techniques into a field stop layer region ofthe semiconductor device to be formed so that an average carbonconcentration within the drift layer region is lower than an averagecarbon concentration within the field stop layer region.

For example, the drift layer region and the field stop layer region maybe formed by two independent implant and annealing processes. Theimplant process for the drift layer may comprise an implant of protonswith one or more implant energies and the annealing process for thedrift layer may comprise tempering according to a defined temperatureprofile (e.g., with a maximal temperature of substantially 490° C.). Theimplant process for the field stop layer may comprise an implant ofprotons with one or more implant energies and the annealing process forthe field stop layer may comprise tempering according to a definedtemperature profile (e.g., with a maximal temperature of substantially400° C. or 420° C.).

FIG. 4 shows a schematic cross section of a Mesa-insulated gate bipolartransistor structure 400. The Mesa-insulated gate bipolar transistorstructure 400 comprises a collector layer 460 (e.g., dopingconcentration of 1e16 to 1e18/cm²) and a backside collector metal layer462 for an electrical contact 464 to the collector layer 460 of theMesa-insulated gate bipolar transistor structure 400 at a backside ofthe Mesa-insulated gate bipolar transistor structure 400. Further, theMesa-insulated gate bipolar transistor structure 400 comprises a driftlayer 470 adjacent to the collector layer 460 and a body layer (e.g.,deposited or implanted) comprising body areas 480 (e.g., dopingconcentration of 1e17 to 1e19/cm² adjacent to the drift layer 470 (e.g.,doping concentration of 5e12 to 1e14/cm²). Additionally, theMesa-insulated gate bipolar transistor structure 400 comprises sourceareas 485 in contact to a source metal layer 486 for an electricalcontact 487 adjacent to the body areas 480. Additionally, also the bodyareas 480 may be in contact to a source metal layer 486, for example.Further, trenches comprising gates 490 (e.g., poly silicon gates)reaching vertically through the body layer are arranged with predefinedlateral distance to each other. The gates can be electrically connectedthrough a gate wiring 492 (not shown). Optionally, the Mesa-insulatedgate bipolar transistor structure 400 may comprise a field stop layerbetween the drift layer 470 and the collector layer 460.

The Mesa-insulated gate bipolar transistor structure 400 comprises bodyareas representing Mesa structures. A Mesa structure comprises asignificantly larger (e.g., more than 5 times larger or more than 10times larger) dimension in one lateral direction than in another lateraldirection (e.g., orthogonal lateral direction).

More details and aspects of a semiconductor device with one or moreMesa-insulated gate bipolar transistor structures 400 semiconductorsubstrate, implementing a varying carbon concentration) are mentioned inconnection with the proposed concept or one or more examples describedabove or below (e.g., FIGS. 1 to 3 or 5 to 6). The semiconductor deviceshown in FIG. 4 may comprise one or more additional optional featurescorresponding to one or more aspects of the proposed concept or one ormore examples described above or below.

FIG. 5 shows examples of two possible distributions 511 and 521 ofcarbon within a semiconductor substrate in the region of the field stoplayer 540. The field stop layer 540 may comprise a thickness between 3μm and 50 μm or between 5 and 30 μm and may be located between a driftlayer 530 (e.g., thickness between 40 μm and 220 μm depending on theblocking voltage of the semiconductor device to be formed) and acollector layer 550 (e.g., comprising a thickness between 200 nm and 500nm).

The diagram indicates the variation of the concentration of hydrogeninduced donors HD and carbon concentration (in arbitrary units) over thedepth (in arbitrary units) measured orthogonal to a front side or backside of the semiconductor substrate.

The semiconductor device shown in FIG. 3, 4, or 5 may comprise a fieldstop zone with a field stop profile 520 shown in FIG. 5.

FIG. 5 shows a comparison of a conventionally generated proton fieldstop profile 510 (concentration of hydrogen induced donors HD) with acorresponding carbon distribution 511 with an example of a proposedfield stop profile 520 (concentration of hydrogen induced donors HD) andcorresponding carbon distribution 521 respectively. Profile 521 shows asupportive CiOi-H-related doping induced by the incorporation ofadditional carbon 521. In this simulation, the implanted doping dose andannealing conditions were the same. Alternatively, the carbonconcentration can be intentionally approximately homogeneously enhancedover the whole vertical extent of the wafer to obtain a higher dopinglevel for the field stop zone and a smaller difference between thedoping concentration of the doping peaks and the neighbouring minima(e.g., resulting in an improved smoothness of the field stop profile andwith it in an improved softness during tum-off of the devices) for givenimplantation doses and annealing conditions, for example.

FIG. 6 shows a flow chart of a method for forming a semiconductordevice. The method 600 comprises implanting 610 a first defined dose ofprotons into a first semiconductor wafer and tempering 620 the firstsemiconductor wafer according to a first defined temperature profile. Atleast one of the first defined dose of protons and the first definedtemperature profile is selected depending on a carbon-related parameterindicating information on a first carbon concentration within at least apart of the first semiconductor wafer. Further, the method 600 comprisesimplanting 630 a second defined dose of protons into a secondsemiconductor water and tempering 630 the second semiconductor wateraccording to a second defined temperature profile. At least one of thesecond defined dose of protons and the second defined temperatureprofile is selected depending on a carbon-related parameter indicatinginformation on a second carbon concentration within at least a part ofthe second semiconductor wafer. Further, the first carbon concentrationis different from the second carbon concentration (e.g., by more than10% of the first carbon concentration, more than 50% of the first carbonconcentration or at least by a factor of 2 for a mean value).

By adapting the defined dose of protons to be implanted and/or thedefined temperature profile used for tempering the semiconductor waferbased on the carbon concentration of the semiconductor wafer, it may beenabled to use semiconductor substrates with different carbonconcentration for forming different semiconductor devices or samesemiconductor devices.

More details and aspects of the method 600 (e.g., semiconductor wafer,implementing a varying carbon concentration, incorporating carbon,carbon related parameter) are mentioned in connection with the proposedconcept or one or more examples described above or below (e.g., FIGS. 1to 5). The method 600 may comprise one or more additional optionalfeatures corresponding to one or more aspects of the proposed concept orone or more examples described above or below.

Some embodiments relate to a method for increasing the doping efficiencyof proton irradiation. An increase of the doping efficiency and/or anadjustment of the profile shape of the so called proton doping may beachieved by a targeted addition of a defined carbon concentration in thesemiconductor crystal.

For example, the doping efficiency of donors produced by a protonirradiation in combination with a suitable tempering may be increased inorder to reduce the required proton dose and consequently the processcosts and/or to increase the degree of freedom for adjusting differentdoping profile shapes.

For example, a defined carbon concentration may be inserted into theregion of the drift zone of a device to be doped (e.g., IGBT) in orderto increase the donor concentration achievable by a specific proton doseand tempering through the generation of complexes resulting from asuitable annealing process.

According to an aspect, carbon may be diffused to the depth of the fieldstop (e.g., from the front side), for example, controlled by the solidstate solubility of substitutional carbon in silicon so that asufficient reproducibility and lateral homogeneity of the dopingconcentration in the drift zone may exist. The diffusion constant ofsubstitutional carbon is shown in FIG. 8. Additionally, interstitialcarbon may be used for utilization of the desired effect (e.g.,increasing implant efficiency).

The carbon diffusion (into the semiconductor) may be integrated in theprocess sequence so that the incorporated carbon is diffused deep enoughinto the semiconductor wafer and is not significantly diffused outafterwards, for example. According to an aspect, the substitutionalcarbon is diffused (into the semiconductor) at the beginning of theprocess.

Alternatively, the carbon may be incorporated in the silicon at thebeginning of the processing. For example, this may be achieved by acorresponding addition of carbon during the crystal growth process. Thestarting concentration of carbon may be determined, if the solid statesolubility of carbon in silicon is underrun. This may be done by aninfrared (IR) measurement or alternatively by a forerunner wafer usedfor determining the doping change due to the present carbon at a protonimplant. The measurement result may be transferred to a larger number ofwafers due to the known segregation behavior of carbon.

Alternatively, the carbon may be deposited on to the wafer by anepitaxial layer. The carbon may be incorporated in a defined way in thelayer profile during the growth. A variety of possible doping profilesmay be implemented by a targeted vertical variation of the carbonconcentration.

The carbon may mainly (e.g., more than 90% or more than 99%) exist inits substitutional form within the silicon crystal lattice prior to theproton implantation step. In this way, it may be achieved that theadditionally incorporated donor concentration may be proportional to theimplant and tempering parameters so that a reproducible effect may beachieved.

Interstitial silicon atoms may be generated additionally to theproton-induced donors and lattice vacancies during the proton implantand the following tempering step (e.g., at temperatures between 300° C.and 550° C. or between 350° C. and 500° C.). The interstitial siliconatoms may diffuse with a comparable fast diffusion constant already atroom temperature. The existing substitutional carbon may function as agetter center for the free interstitial silicon atoms, thus interstitialcarbon Ci may be generated. The transfer from Cs to Ci can be alsoinduced by the energy transfer of the implanted protons. Theinterstitial carbon may in turn build up desired CiOi-H complexes withavailable oxygen and the implanted hydrogen. The process may be limitedto the initial concentration and distribution of the substitutionalcarbon Cs, since the concentration of interstitial oxygen Oi within a.utilized substrate may be higher than the concentration ofsubstitutional carbon Cs. In this way, the resulting doping profile maybe adjustable with an additional degree of freedom. For example, theCiOi-H donors may be generated in a defined depth and/or profileadditionally to the proton-induced donors and may as a consequenceeffectively increase and/or stabilize the doping efficiency of theproton doping. For example, the concentration of interstitial oxygen Oimay be larger than 1*10¹⁷ cm⁻³ and the concentration of substitutionalcarbon Cs may be lower than 1*10¹⁶ for MCZ (magnetic-field-inducedCzochralski) substrate.

Alternatively or additionally, the effect may be controlled by atargeted adjustment of the interstitial carbon Ci profile. For example,interstitial carbon Ci may be generated after a diffusion ofsubstitutional carbon Cs by an irradiation with electrons, alphaparticles, helium or protons. The depth of the maximal effect may becontrolled by the energy of the irradiation, for example. Alternatively,the interstitial carbon Ci concentration diffused into the substrate maybe utilized which may be determined by the diffusion parameters ofcarbon and the final thickness of the substrate, for example.

The influence of the surface as a drain for the carbon, or during theproton implant to the distribution of the interstitial silicon atoms maybe used for the adjustment of the profile shape of the interstitialcarbon Ci.

For example, turtle-shaped doping profiles (or other shapes) may begenerated (e.g., in the drift zone) by combined in- and out diffusion ofcarbon. For example, the doping maximum of the drift zone doping may belocated approximately at half of the depth of the drift zone (e.g., inthe middle third of the drift zone or between 40% and 60% of the depthof the drift layer) to improve the switch-off properties. Alternatively,the doping maximum may be shifted to another position of the drift zoneby a suitable selection of the parameters of diffusion of carbon intothe substrate or out of the substrate.

For example, also a targeted gradient of the drift zone doping may beadjusted by implementing a defined profile of carbon atoms diffusinginto the substrate by the parameters of diffusion of carbon into thesubstrate or out of the substrate (e.g., annealing temperature or time).For example, the switch-off process of power semiconductors, theblocking capability and/or the cosmic radiation stability may beimproved or optimized by a defined presetting of a gradient for thedrift zone profile or by the implementation of a turtle-shaped dopingprofile.

According to an aspect, the doping efficiency of proton-induced fieldstop zones may be improved by a defined front side diffusion of carbonatoms into the substrate. In this way, the waviness or ripple ofprofiles of multi-step field stop zones generated by multipleimplantations utilizing several implant energies may be significantlyreduced, for example. This may be explained on one hand by the gradualcourse of the carbon concentration and the consequently inducedadditional doping and on the other hand by the reduced vacancyconcentration between the doping maxima which significantly facilitatethe transition from substitutional carbon to interstitial carbon. Anexample for a doping profile smoothed by carbon incorporation is shownin FIG. 5.

According to an aspect, the proposed drift zone doping and/or field stopdoping may be implemented within material pre-doped with donor atomslike e.g., phosphorus, arsenic or antimony during the crystal growth orby neutron transmutation doping, for example.

Alternatively or additionally, carbon may be diffused into the substratefrom the wafer back side. The diffusion constant of the substitutionalcarbon for larger wafer diameters (e.g., 8″ or 12″) for thin wafers maybe too low so that the carbon may be diffused into the substrateinterstitially and therefore with low solubility. The diffusion constantof interstitial carbon 910 exceeds the diffusion constant ofsubstitutional carbon 810 by several orders of magnitude (e.g., FIGS. 8and 9).

Additionally or alternatively, carbon may be incorporated targeted in adefined depth during epitaxy. The epitaxy process may be interruptedonce or several times to generate a variety of profiles. The carbon canbe introduced from the gas phase during the epitaxial deposition or/andby carbon implantation steps prior to the epitaxial deposition and/orduring the interruptions of the epitaxial deposition.

The correlation of the course of the doping profile with the content ofcarbon in defined positions of the device (e.g., vertical profilecourses) may be done with space-resolved DLTS (deep-level transientspectroscopy) and/or IR (infrared) measurements.

Example embodiments may further provide a computer program having aprogram code for performing one of the above methods, when the computerprogram is executed on a computer or processor. A person of skill in theart would readily recognize that acts of various above-described methodsmay be performed by programmed computers. Herein, some exampleembodiments are also intended to cover program storage devices, e.g.,digital data storage media, which are machine or computer readable andencode machine-executable or computer-executable programs ofinstructions, wherein the instructions perform some or all of the actsof the above-described methods. The program storage devices may be,e.g., digital memories, magnetic storage media such as magnetic disksand magnetic tapes, hard drives, or optically readable digital datastorage media. Further example embodiments are also intended to covercomputers programmed to perform the acts of the above-described methodsor (field) programmable logic arrays ((F)PLAs) or (field) programmablegate arrays ((F)PGAs), programmed to perform the acts of theabove-described methods.

The description and drawings merely illustrate the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its spirit and scope. Furthermore,all examples recited herein are principally intended expressly to beonly for pedagogical purposes to aid the reader in understanding theprinciples of the disclosure and the concepts contributed by theinventor(s) to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass equivalents thereof.

Functional blocks denoted as “means for . . . ” (performing a certainfunction) shall be understood as functional blocks comprising circuitrythat is configured to perform a certain function, respectively. Hence, a“means for s.th.” may as well be understood as a “means configured to orsuited for s.th.”. A means configured to perform a certain functiondoes, hence, not imply that such means necessarily is performing thefunction (at a given time instant).

Functions of various elements shown in the figures, including anyfunctional blocks labeled as “means”, “means for providing a sensorsignal”, “means for generating a transmit signal.”, etc., may beprovided through the use of dedicated hardware, such as “a signalprovider”, “a signal processing unit”, “a processor”, “a controller”,etc. as well as hardware capable of executing software in associationwith appropriate software. Moreover, any entity described herein as“means”, may correspond to or be implemented as “one or more modules”,“one or more devices”, “one or more units”, etc. Men provided by aprocessor, the functions may be provided by a single dedicatedprocessor, by a single shared processor, or by a plurality of individualprocessors, some of which may be shared. Moreover, explicit use of theterm “processor” or “controller” should not be construed to referexclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (DSP)hardware, network processor, application specific integrated circuit(ASIC), field programmable gate array (FPGA), read only memory (ROM) forstoring software, random access memory (RAM), and non-volatile storage.Other hardware, conventional and/or custom, may also be included.

It should be appreciated by those skilled in the art that any blockdiagrams herein represent conceptual views of illustrative circuitryembodying the principles of the disclosure. Similarly, it will beappreciated that any flow charts, flow diagrams, state transitiondiagrams, pseudo code, and the like represent various processes whichmay be substantially represented in computer readable medium and soexecuted by a computer or processor, whether or not such computer orprocessor is explicitly shown.

Furthermore, the following claims are hereby incorporated into theDetailed Description, where each claim may stand on its own as aseparate embodiment. While each claim may stand on its own as a separateembodiment, it is to be noted that—although a dependent claim may referin the claims to a specific combination with one or more otherclaims—other embodiments may also include a combination of the dependentclaim with the subject matter of each other dependent or independentclaim. Such combinations are proposed herein unless it is stated that aspecific combination is not intended. Furthermore, it is intended toinclude also features of a claim to any other independent claim even ifthis claim is not directly made dependent to the independent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or claims may not be construedas to be within the specific order. Therefore, the disclosure ofmultiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments a single act may include ormay be broken into multiple sub acts. Such sub acts may be included andpart of the disclosure of this single act unless explicitly excluded.

What is claimed is:
 1. A semiconductor device, comprising at least onetransistor structure comprising: an emitter or source terminal; and acollector or drain terminal, wherein an interstitial carbonconcentration within a semiconductor substrate region located betweenthe emitter or source terminal and the collector or drain terminalvaries between the emitter or source terminal and the collector or drainterminal, wherein the interstitial carbon concentration corresponds to aconcentration of carbon atoms which assume normally unoccupied sites ina crystal structure of the semiconductor substrate region, whereinC_(x)iO_(x)i-H complexes are built-up from the interstitial carbonconcentration with oxygen and hydrogen available in the semiconductorsubstrate region.
 2. The semiconductor device of claim 1, wherein the atleast one transistor structure is an insulated gate bipolar transistorarrangement comprising a semiconductor structure comprising a collectorlayer, a drift layer, a plurality of body areas, a plurality of sourceareas and a plurality of gates, wherein the plurality of source areasand the drift layer comprise dopants of a first conductivity type,wherein the plurality of body areas and the collector layer comprisedopants of a second conductivity type, and wherein the plurality ofgates are arranged so that the plurality of gates is configured to causea conductive channel between the source areas and the drift layerthrough the body areas.
 3. The semiconductor device of claim 1, whereina semiconductor substrate of the semiconductor device includes thesemiconductor substrate region and has a thickness of less than 200 μm.4. The semiconductor device of claim 1, wherein the interstitial carbonconcentration within at least one part of the semiconductor substrateregion is higher than 1*10¹⁴ cm⁻³.
 5. The semiconductor device of claim1, wherein the interstitial carbon concentration within at least onepart of the semiconductor substrate region is higher than 5*10¹⁵ cm⁻³.6. The semiconductor device of claim 1, wherein the interstitial carbonconcentration within at least one part of the semiconductor substrateregion is higher than 1*10¹⁶ cm⁻³.
 7. The semiconductor device of claim1, wherein the interstitial carbon concentration within thesemiconductor substrate region is an average interstitial carbonconcentration or a maximal interstitial carbon concentration.
 8. Thesemiconductor device of claim 1, wherein the interstitial carbonconcentration within at least one part of the semiconductor substrateregion is lower than 1*10¹⁴ cm⁻³.
 9. The semiconductor device of claim1, wherein the interstitial carbon concentration within at least onepart of the semiconductor substrate region is lower than 5*10¹⁵ cm⁻³.10. The semiconductor device of claim 1, wherein the semiconductorsubstrate region comprises silicon, silicon carbide, gallium arsenide,or gallium nitride.
 11. The semiconductor device of claim 1, wherein theinterstitial carbon concentration within the semiconductor substrateregion has a maximal interstitial carbon concentration of less than2*10¹⁶ cm⁻³ and a minimal interstitial carbon concentration of more than1*10¹⁴ cm⁻³.
 12. The semiconductor device of claim 1, wherein theinterstitial carbon concentration within the semiconductor substrateregion has a minimal interstitial carbon concentration and a maximalinterstitial carbon concentration of more than twice the minimalinterstitial carbon concentration.
 13. The semiconductor device of claim1, wherein the at least one transistor structure further comprises adrift layer between the emitter or source terminal and the collector ordrain terminal, wherein the semiconductor substrate region has anincreased interstitial carbon concentration within the drift layer incomparison to other regions of the semiconductor substrate region. 14.The semiconductor device of claim 1, wherein the interstitial carbonconcentration within the semiconductor substrate region varies fordifferent depths within the semiconductor substrate region.
 15. Thesemiconductor device of claim 14, wherein the interstitial carbonconcentration within the semiconductor substrate region varies between1*10¹⁴ cm⁻³ and 2*10¹⁶ cm⁻³ for the different depths within thesemiconductor substrate region.
 16. The semiconductor device of claim14, wherein the interstitial carbon concentration within thesemiconductor substrate region varies between 1*10¹⁴ cm⁻³ and 1*10¹⁷ forthe different depths within the semiconductor substrate region.
 17. Thesemiconductor device of claim 14, wherein the interstitial carbonconcentration within the semiconductor substrate region varies between1*10¹⁵ cm⁻³ and 5*10¹⁵ cm⁻³ for the different depths within thesemiconductor substrate region.
 18. A semiconductor device, comprisingat least one transistor structure comprising: an emitter or sourceterminal; a collector or drain terminal; a drift layer between theemitter or source terminal and the collector or drain terminal; and afield stop layer between the drift layer and the collector or drainterminal, wherein a carbon concentration within a semiconductorsubstrate region located between the emitter or source terminal and thecollector or drain terminal varies between the emitter or sourceterminal and the collector or drain terminal, wherein the field stoplayer has an average carbon concentration of at least twice an averagecarbon concentration of the drift layer.
 19. A semiconductor device,comprising at least one transistor structure comprising: an emitter orsource terminal; a collector or drain terminal; a drift layer betweenthe emitter or source terminal and the collector or drain terminal; anda field stop layer between the drift layer and the collector or drainterminal, wherein an average carbon concentration within the drift layeris lower than an average carbon concentration within the field stoplayer.
 20. A semiconductor device, comprising at least one transistorstructure comprising: an emitter or source terminal; and a collector ordrain terminal, wherein an interstitial carbon concentration within a Sisubstrate region located between the emitter or source terminal and thecollector or drain terminal varies between the emitter or sourceterminal and the collector or drain terminal, wherein the interstitialcarbon concentration corresponds to a concentration of carbon atomswhich assume normally unoccupied sites in a crystal structure of the Sisubstrate region.